This study investigated the galloping behavior of a slender square-section cylinder inclined from the vertical direction by a series of angles. Both aeroelastic tests and pressure measurements were performed on the cylinder with forward inclinations (inclined to the upwind direction), a vertical attitude and backward inclinations (inclined to the downwind direction). Results from the aeroelastic tests show that the galloping amplitude of the cylinder decreases substantially with increasing the forward inclination angle. Unlike the forward inclination case, not all the backward inclined cylinders oscillate at an amplitude smaller than the vertical cylinder does. The galloping amplitude of the cylinder with a small backward inclination angle is significantly larger than that of the vertical cylinder, whereas the cylinder with a large backward inclination angle exhibits a lower amplitude. Comparing aeroelastic galloping amplitudes with those predicted by the quasi-steady theory shows that the quasi-steady theory is applicable to predict the variation trend of the galloping behavior induced by both forward and backward inclinations, although it is unable to give accurate predictions on galloping amplitudes of all the inclined cylinders. &